Method of tin plating and activated fatty oil composition therefor



METHOD OF TIN PLATING AND ACTIVATED FATTY OIL COMPOSITION THEREFORLudwig Rosenstein and Manuel H. Gorin, San Francisco, Calif.

No Drawing. Application August 13, 1952-, Serial No. 304,215

18 Claims. (Cl. 117-114) This invention relates to an improvement in theprocess of making hot-dipped tinplate.

Tinplate is made by two prevailing processes; one of these, known as theelectrolytic tinning process, consists in depositing tinelectrolytically on sheets of steel and then subjecting said platedsheet to a temperature above the melting point of tin. The secondprocess, known as hot-dip tinning, consists of passing a sheet of steelsuccessively through (a) a flux, (b) a body of molten tin, and (c) abody of oil overlying the body of molten tin. Our invention bears mainlyon the second of these processes and more specifically to improvement onthe step (c).

The steel industry has for many years used one oil almost exclusively assuitable oil for the above mentioned step (c) of the hot-dip tinningprocess; this is palm oil. Palm oil is a product derived from the nut ofcertain types of tropical palms and has unique properties with respectto molten tin, said unique properties being that:

1. It keeps the surface of molten tin bright and shiny, probably bykeeping it free of tin oxide.

2. It does not adhere to the tin surface and therefore tinplate emergingout of a layer of palm oil is clean in the sense that it has no morethan a trace of adherent oil.

3. Palm oil is not excessively voltatile.

4. It oxidizes and polymerizes slowly compared with other fatty oils atabout the temperature of molten tin.

When an oil has and exhibits the properties described in i and 2 above,it is called an active oil in the tinplate industry; if the oil does nothave and exhibit these properties, it is called inactive, and is uselessas a bath over the molten tin in the hot-dip process. The relativeactivity of oils is the first measure of their usefulness in this art.

Palm oil is an imported material coming mainly from the East Indies andAfrica. The tin-plate industry has long sought an acceptable substituteamong domestic oils in order to avoid the necessity of importationespecially in times of national emergency and also as a means ofmitigating the historic and wide price fluctuations which have beenencountered. As an indication of the seriousness with which the steelindustry regards this problem, we mention that the American Iron andSteel Institute established a fellowship at the Armour ResearchInstitute, Chicago, Illinois, for a study of possible substitutes forpalm oil. A progress report was made by the American Iron and SteelInstitute entitled Contribution to the Metallurgy of Steel, No. 32, May1949 and this research has been continued under the sponsorship of aDepartment of the United States Government.

We have found ways and means of modifying, by certain additions, anumber of domestic vegetable and animal fats and oils and imparting tothem properties equal, and in some cases superior, to those of palm oilfor use in hot-dip tinning.

Briefly, we have found that the addition of certain resinous substancesin varying proportionsaccomplishes 2,746,884 Patented May 22, 1956 thedesired objective. Compositions of resinous substances dissolved in oilsare old and well known in the art of varnish making, but in these knowncompositions the resinous substances are compounded with drying oils, i.e., with oils containing sufficient glycerides of unsaturated fattyacids so that oxygen is rapidly absorbed with the formation of films.Linseed oil and tung oil are the outstanding examples of the type ofoils used in varnish making. Such oils are unsuited for hot-dip tinningpurpose. We have found that by mixing certain resinous substances withnon-drying oils, such as ricebran oil, cottonseed oil, tallow, etc., andheating until homogeneous, we obtain compositions which behave towardshot tin surfaces comparably to the way palmoil behaves.

Resinous substances which have been found to impart the desirableproperties include:

1. Gum rosin 2. Wood rosin 3. Ester Gum g 4. High boiling (rosin)fraction of tall oil, also known as liquid rosin 5. Hydrogenated rosin6. Tall oil esters in which the resin acids content are not esterified7. The reaction product of rosin with an aldehyde.

The materials in the above list are natural products (or theirderivatives), all of which have complex structures built upon aphenanthrene skeleton with attachments of one or more carboxyl groups.Physically they are highly viscous, sticky liquids or resinous to glassysolids.

We have mentioned hydrogenated rosin as suited for compounding withnon-drying fatty oils. Rosin has two conjugated double bonds, and thefirst effect of hydrogenation is to add hydrogen at one of the doublebonds, leaving a structure with only one double bond. We have notexperimented with completely hydrogenated rosin; that is, a rosin nolonger containing a double bond, because such material is notcommercially available. We believe, however, that such completelyhydrogenated rosin will function at least as well as the commercialpartially hydrogenated rosin.

The method we used for testing any given composition with regard to itsusefulness for hot dip tinplating is described on page 10 et seq. of thepreviously mentioned Contributions to the Metallurgy of Steel. Briefly,it consists in establishing a molten tin surface in a Petri dish at atemperature somewhat above the melting point of tin and applying to saidsurface a limited quantity of the material to be tested. Inactivesubstances, such as mineral oil and unmodified cotton-seed oil, spreaduniformly over the surface of the molten tin and manifest no reactivitytowards the surface layer. Active substances, such as palm oil, on theother hand, leave considerable areas of the tin surface unwetted andmove vigorously across the surface with a peculiar scouring action,which removes surface layers and leaves a clean, mirror-like surface onthe tin. The distinction between active and inactive substances isunmistakable and the level or degree of activity can be judged by thelength of time that a clear tin surface persists. The activity decreaseswith time and the more rapidly the higher the temperature. Eventuallythe movement ceases and the surface becomes covered uniformly with alayer of oil.

We will now give a number of examples of specific embodiments of ourinvention.

Example I Rice bran oil which was produced by extraction of rice branwith hexane, followed by evaporation of the hexane, was blended with 20%by weight of ordinary wood rosin. This composition was testedsimultaneously with one control of palm-oil and another control ofunmodified rice-bran oil. The temperature was 290-300 C. The palm oilremained active for ten minutes; the rice-bran oil remained active. forsix minutes. Rice-bran oil plus 20% rosin remained active sixteen.minutes.

Examplel illustrates the enhancement of the. activity of rice-bran oil,which by itself has a certain amount of natural. activity; that. is, itis active to some degree without additive.

Example II A hydrogenated cottonseed. oil, commercially known as Crisco,was blended with 5% of a hydrogenated rosin commercially produced byHercules Powder Co. and. known as Staybelitef This was compared withpalm-oil and with uncompounded Crisco at 290 C. Palm oil remained activefourteen minutes, Crisco plus 5% Staybelitc was still active. after 132minutes, but had, through oxidation and polymerization, become veryviscous. Crisco alone showed no activity whatever.

This experiment demonstrates the activation of an oil that has noactivity in itself.

Example 111 Ricebran oil was compounded with 10% by weight of theresinous high-boiling fraction of a refined tall oil. It was comparedwith palm-oil at 290 C., and with ricebran oil to which nothing has beenadded. The palm oil remained active 16 minutes; the untreated rice-branoil remained active 9 minutes; the rice-bran oil+10% tall-oil rosin wasstill active after 36 minutes, but had become quite viscous.

Example IV A tallow of about 35 C. titer to which 5% hydrogenated rosinhad been added was compared at about 290 C. with palm-oil and untreatedtallow. The palmoil remained active l6 minutes; the plain tallowremained active 2-4 minutes; the tallow+5% Staybelite remained active 32minutes.

This illustrates the effect of the same activating agent as in Example Hon another fat.

Example V Palm-oil. was compounded with 5% Staybelite and this blend wascompared with the original uncornpounded palm-oil at 290 C. Thepalm-oil; compounded with Staybelite was one of the most active of allthe preparationsmade to date, as judged by the vigor of the surfacemovement and the brilliancy of the molten tin surface. it remainedactive for an indefinite time, but after about Hi minutes at the hightemperature the movement had become sluggish because of the increasedviscosity of the oil.

This example illustrates the enhancement of activity of palm-oil andlengthening its life by compounding with hydrogenated rosin.

Example VI Refined cotton-seed oil compounded with 10% Staybelite at 290C. was extremely active and remained so for more than 100 minutes,whereas a palm-oil control remained active 16 minutes.

This experiment was designed to shown that refined cotton-seed oil canbe activated similarly to the hydrogenated oil.

Example VI! Hydrogenated cotton-seed oil blended with of a woodrosinwhich had been. reacted with paraformaldehyde to raise its softeningpoint from 64 C. to 84 C., was compared with palm-oil at. 290 C. Afteran initial heating period'of l0 minutes'at 290 C, the compounded oilremained active indefinitely, whereas the palm-oil control remainedactive only 16 minutes.

This experiment was designed to show that an aldehyde modified rosin isa suitable activating compound.

Palm-oil as well as other oils from difierent sources, and evendifferent lots from the same source, behave somewhat difierently towardmolten tin. This accounts for the fact that the palm-oil controlsmentioned in the various examples did not all have the same degree ofactivity when measured as herein described.

We have further found that the way in which the blends of oils andresinous substances are made has a marked effect on the activity'towardmolten tin. We prefer to heat the oils to a temperature of about 150 C.and then add the resinous substance. either as a line powder or smalllumps. The material is kept Well stirred until all resinous substancehas dissolved and is then held quiescent at a temperature between 100and 200 C. for about 1 to 3 hours. The mentioned limits of time andtemperature will cover the majority of practical cases.

Early experiments with crude cotton-seed oil. indicated that it. was notactive and could not. be easily activated by the addition of. resinous.substances, while refined cotton-seed oil responded very well to suchactivation. It was concluded. that the particular sample of crudecottonseed oil, which was very dark in color, contained interferingimpurities. A simple clay-filtration, such as is commonly practiced in.the fatty oil industry to lighten the color, was sufiicient to remove.the interfering impurities, and thereafter the crude oil responded aswell as did the highly refined oil.

While all the resinous materials mentioned impart some degree ofactivity to inactive fatty oils, or enhance the activity of those whichhave varying degrees of natural activity, one preferred embodiment is touse hydrogenated rosin for the activator. We have found that as littleas 1% hydrogenated rosin, blended as described, into hydrogenatedcotton-seed oil (which of itself is substantially inactive) will impartto it a degree of activity which makes it as active as palm-oil.

Early experiments showed that hydrogenated cottonseed oil responded inthe most marked degree to the addition of resinous. substances. Thedifference between hydrogenated and ordinary cotton-seed oil is mainlyin the ratio of unsaturated to saturated fats; that is, more specficallythe ratio of oleins to stearins. The addition of a high stearin fat tocotton-seed oil will change this ratio in somewhat the same sense ashydrogenation. A blend of about 30%-40% tallow with cotton-seed oil willrespond to blending with resinous substances about as well ashydrogenated cotton-seed oil.

One composition well suited for a tinning oil is:

Another composition which We have found especially desirable is:

Per cent Clarified rice-bran oil 95-995 Hydrogenated resin /2- 5Rice-bran oil is somewhat more heat-stable than cottonseed oil, and forthis reason may be preferred, although the eventual choice of theparticular non-drying fatty oil to compound may depend on costas much ason its heat-stability.

A third. useful composition is:

Percent Hydrogenated cotton-seed oil -98 Rosinous fraction of tall-oil2-15 Our invention is not confined to these compositions, which aregiven byway of a: practical example, but includes various blends ofnon-drying fatty oils compounded with resinous substances.

While we have designated certain compositions of fatty, non-drying oilswith resinous substances especially suitable for use in production oftin-plate, we do not confine our invention to these examples or to thissole purpose. Other compositions of these classes of compounds can beused, and usefulness can be extended to production of terneplate, and tothe finishing operation characteristic of the electrolytic tin-plateprocess.

The term fatty oils or fatty oil as used in this specification and inthe claims designates those commercial products which are essentiallyglycerides of high-molecular weight fatty acids, and are of plant oranimal origin. This term, which is commonly used in the trade,distinguishes these substances from any of the oily or waxy productsderived from petroleum. (See for example Chemicals of Commerce, Snelland Snell, D. Van Nostrand and Company, New York, 2nd edition, theheading on p. 348.)

We claim:

1. A new composition of matter for use, cojointly with molten tin, intin-plate production containing only a solution in a non-drying fattyoil of a resinous organic substance selected from the group comprisinggum rosin, wood rosin, hydrogenated rosin, rosin esters, the rosinfraction of tall-oil, and rosin modified by treatment with an aldehyde;said resinous substance constituting 1% to 20% of the composition.

2. A composition of matter as in claim 1 wherein the fatty oil iscotton-seed oil.

3. A composition of matter as in claim 1 wherein the fatty oil ishydrogenated cotton-seed oil.

4. A composition of matter as in claim 1 wherein the fatty oil istallow.

5. A composition of matter as in claim 1 wherein the fatty oil isrice-bran oil.

6. A composition of matter as in claim 1 wherein the fatty oil ispalm-oil.

7. A composition of matter as in claim 1 wherein the resinous organicsubstance is gum rosin.

8. A composition of matter as in claim 1 wherein the resinous organicsubstance is wood rosin.

9. A composition of matter as in claim 1 wherein the resinous organicsubstance is hydrogenated rosin.

10. A composition of matter as in claim 1 wherein the resinous organicsubstance is aldehyde treated rosin.

11. A composition of matter as in claim 1 wherein the resinous organicsubstance is substantially the resinous fraction of tall-oil.

12. A composition of matter useful in tin-plate production containingonly a solution of hydrogenated rosin in a fatty non-drying oil, saidsolution containing from 1% to 20% of said hydrogenated rosin.

13. A composition of matter as in claim 12 wherein the oil ishydrogenated cotton-seed oil.

14. A composition of matter as in claim 12 wherein the oil is rice-branoil.

15. A composition of matter as in claim 12 wherein the oil is tallow.

16. A composition of matter as in claim 12 wherein the oil is palm-oil.

17. In a process of tinning metal plates by passing said plates througha body of molten tin, the step comprising passing the plates as theyemerge from the body of molten tin through a body floating on saidmolten tin consisting essentially of a fatty non-drying oil which hasdissolved therein, in an amount from 1% to 20%, a resinous substanceselected from the group rosin, wood rosin, hydrogenated rosin, rosinesters, the rosin fraction of tall oil, and rosin treated withparaformaldehyde.

18. In a process as in claim 17 wherein the non-drying oil is tallow andthe resinous substance is hydrogenated IOSlIl.

References Cited in the file of this patent UNITED STATES PATENTS1,242,532 Dreymann Oct. 9, 1917 2,136,681 Fulton et a1. Nov. 15, 19382,275,583 Catlow Mar. 10, 1942 2,293,580 Walker Aug. 18, 1942 2,350,977Agthe June 13, 1944 2,357,016 Miller Aug. 29, 1944 2,395,925 Walton etal. Mar. 5, 1946

17. IN A PROCESS OF TINNING METAL PLATES BY PASSING SAID PLATES THROUGHA BODY OF MOLTEN TIN, THE STEP COMPRISING PASSING THE PLATES AS THEYEMERGE FROM THE BODY OF MOLTEN TIN THROUGH A BODY FLOATING ON SAIDMOLTEN TIN CONSISTING ESSENTIALLY OF A FATTY NON-DRYING OIL WHICH HASDISSOLVED THEREIN, IN AN AMOUNT FROM 1% TO 20%, A RESINOUS SUBSTANCESELECTED FROM THE GROUP ROSIN, WOOD ROSIN, HYDROGENATED ROSIN, ROSINESTERS, THE ROSIN FRACTION OF TALL-OIL, AND ROSIN TREATED WITHPARAFORMALDEHYDE.